The present invention relates generally to smokestacks for combustion chambers such as boilers, furnaces or the like, and more particularly to exhaust control structure for such smokestacks.
A smokestack typically comprises a lower portion communicating with the exhaust port of a combustion chamber, such as a boiler, and a top opening communicating with the atmosphere. Among the problems arising with conventional smokestacks are the condensation of water vapor from the exhaust gas stream within the smokestack, causing corrosion or other adverse effects in the smokestack. Another problem is pulsations within the boiler, accompanied by a pulsating exhaust stream coming out of the top of the smokestack, indicative of less than optimum combustion in the boiler.
Holland, U.S. Pat. No. 3,706,290, describes structure for reducing the above-noted drawbacks. This structure is in the form of an exhaust control device overlying the top opening of the smokestack and in the form of a substantially flat plate having a sharp-edged circular orifice overlying the interior of the smokestack. This device causes the formation of an annular insulating blanket of exhaust gases around the periphery of the smokestack interior and a uniformly flowing stream of exhaust gases passing steadily up the center of the annulus. The net effect of this is to avoid condensation of water vapor within the smokestack and to eliminate pulsating within the boiler and from the smokestack. These effects in turn promote a cleaner, hotter exhaust leaving the smokestack, improve the completeness of combustion, reduce fuel consumption and reduce uncombusted or pungent gases in the exhaust stream.
In order to best accomplish the advantages of the device described in the Holland patent, the exhaust control orifice should have a cross-sectional area corresponding to the effective size of the exhaust port in the combustion chamber or boiler. When more than one boiler is being used, the orifice should have a size corresponding to the combined cross-sectional areas of all the exhaust ports on all the boilers.
However, when there is a change in the number of boilers operating or when there is a change in the operating conditions in a given boiler, the orifice size which is optimum for an initial set of conditions may no longer be optimum.
The considerations involved in the selection of the exhaust control orifice size and the advantages flowing therefrom are described in greater detail in said Holland U.S. Pat. No. 3,706,290, and the disclosure thereof is incorporated herein by reference.